I have recently had a couple of motors in my shop that have had damage from pre ignition . They have pitting on the top of the piston and button. Also both the owners experienced glowplug failures prior to this.

I would normally think this is from over compression, or using too hot of a plug ?? Is this correct ? Could there be other reasons for this ?

You forgot one Item. To short of a tuned pipe will also cause detonation. If the head shimming is correct for the percentage nitro used and the engine continues to detonate suspect the pipe is to short.

Well the way i understand it is basicly the same as in a 4 stroke car engine. If you have too lean a mixture it causes the cylinder temp to become to great and causes pre-ignition, however in a car engine what usually happens is the extra heat from the lean mixture causes hot spots on pistons or valves and that is what cause the fuel miture to ignite prematurly, the other side of the coin is that the pitting could have also been caused from the element when it expired bouncing around inside the liner (not likely but a possability).

and can be from running too much castor oil in the fuel blend...i got marks like smoke marks on the top of my piston and on the sides and stuff from running way too much fuel..like 7 gallons before i cleaned her again...i recommend that the engine be pulled apart and cleaned out (or polished) so that the carbon buildup is removed asmuch as possible...

I am having trouble with detonation on my .12 engine. What should the shim be on a .12? I think it may be shimmed wrong. I only get about 4 tanks on one glow plug if i am lucky. My engine also doesnt hold a tune. One week i ran it and it ran fine, had a good tune. The next week i started it up and about 5 laps later it over heated and when i checked the temp it was 275.

If its a .21 engine 0.4mm head clearance is way to small. 0.7 is normal.

Cheers

For a very few times. I agree with M7H... All depends on many factors:

- Nitro content
- Relative humidity
- Altitude over the sea level.

One of the best gadgets one can bring to a track is a small weather station (Oregon Scientific have some very nice ones) and start to get some notes about the temp, height and rel. humidity during the use of our engines and start messing with the combustion chamber height.

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Cheers,
Corse-R
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[quote=MugenDrew;2684554]BATTERIES are for FLASH LIGHTS, gasoline is for cleanin parts, alcohol is for me to drink and well NITRO...everybody know thats for racing.[/quote] :D:D:D

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